Multi-component flux measurement system and method for urban areas based on eddy covariance method

Abstract

The present application discloses a system and method for measuring multi-component flux in urban areas based on eddy covariance method, and relates to the technical field of multi-component flux measurement in urban areas. The system comprises: a multi-satellite clock synchronization timing module, a high-altitude micrometeorological measurement module, an off-site sample transmission module, a ground multi-component concentration measurement module, a cumulative covariance time lag determination module and a multi-component flux calculation module. The system can acquire a vertical wind speed time series at high altitude, and simultaneously transmit the high-altitude air to the ground multi-component concentration measurement module corresponding to each component to be measured located on the ground, acquire a concentration time series corresponding to each component to be measured, and unify the time axes of the vertical wind speed time series and the concentration time series, further determine the time lag corresponding to each component to be measured, and finally calculate the flux of each component to be measured. The present application can be used to guide the flux measurement of multiple gas components in urban areas.

Description

Technical Field

[0001] The present application relates to the technical field of multi-component flux measurement in urban areas, and in particular to a multi-component flux measurement system and method in urban areas based on an eddy covariance method. Background Art

[0002] Quantifying and characterizing the material exchange process in the ecological environment is an important means to study the material cycle, energy exchange and productivity assessment of the ecosystem. Flux refers to the amount of material exchange per unit area per unit time, and is a key indicator for quantifying the material cycle in the ecosystem. The eddy covariance method is a micrometeorological technology that can directly measure the material exchange between the ground (such as vegetation, soil, lakes, etc.) and the atmosphere. It calculates the turbulence-dominated transport volume by measuring and calculating the covariance of the concentration pulsation of the component and the vertical wind speed pulsation, that is, determining the flux. It has become a standardized and normalized method for measuring flux at the ecosystem scale and has been widely used throughout the world. The eddy covariance method requires setting up sampling points in the constant flux layer, and using high-frequency measuring instruments at the sampling points to carry out high-frequency synchronous measurement of the concentration of the measured substance and the vertical wind speed, collect high-frequency data, and then calculate the mean concentration and the mean vertical wind speed within a certain time window, and express all high-frequency data within the time window as average terms and pulsation terms. Finally, the average flux of the measured substance can be expressed as the covariance of the concentration pulsation and the vertical wind speed pulsation of the measured substance.

[0003] In order to quantify and characterize the material exchange of typical ecosystems, a relatively standardized flux measurement method based on the eddy covariance method has been formed. This method is mainly aimed at ecosystems with relatively low plant canopies such as farmland, grassland, and shrubs. The specific operation steps are as follows: select a flat area in the target ecosystem, build a simple flux observation tower (generally 3-5 meters), and fix a crossbar on the top of the observation tower. Install an ultrasonic anemometer on the crossbar to ensure that the height of the ultrasonic anemometer is greater than 2-3 times the height of the plant canopy. After properly leveling the ultrasonic anemometer, use the ultrasonic anemometer to carry out high-frequency measurement and collect high-frequency vertical wind speed data. At the same time, at the same height of the ultrasonic anemometer, install the sampling port of the gas concentration measuring instrument. The sampling port is as close to the center point of the measurement area of ​​the ultrasonic anemometer as possible. The gas concentration measuring instrument can be installed together with the ultrasonic anemometer at the crossbar at the top of the observation tower, or it can be placed near the ground of the observation tower. The gas concentration measuring instrument is connected to the sampling port at the top of the observation tower through a pipeline. The length of the pipeline is generally not more than 5 meters. Use the gas concentration measuring instrument to carry out high-frequency measurement and collect high-frequency concentration data. The signals of the ultrasonic anemometer and the gas concentration measuring instrument are connected to the data collector to complete the time axis synchronization and data recording of high-frequency data (i.e., high-frequency vertical wind speed data and high-frequency concentration data). In order to properly handle the time lag phenomenon, the maximum covariance method is used to determine the time lag, and the concentration time axis is corrected accordingly, and the covariance calculation of subsequent concentration pulsation and vertical wind speed pulsation is carried out to obtain the flux results.

[0004] As an important part of the ecosystem, cities not only emit more than 70% of greenhouse gases, but are also the areas with the most serious air pollution. Research on their material cycles and emission characteristics is of great significance to the improvement of urban air quality. However, as the most complex man-made ecological environment, compared with ecosystems such as grasslands and farmlands, it is extremely challenging to use the eddy covariance method to carry out flux measurements of multiple gas components in urban areas. The existing standardized flux measurement methods have great technical constraints and methodological deficiencies. This is because when conducting flux measurements, the sampling points need to be set at a high enough altitude to ensure that flux measurements are carried out in the normal flux layer. In urban areas, the height of buildings is much higher than the height of the vegetation canopy in ecosystems such as grasslands and farmlands. Therefore, when measuring flux in urban areas, the sampling points need to be set at an altitude of tens to hundreds of meters, such as the high-altitude observation platform of a city tower. When conducting coordinated flux measurements of multiple gas components, a series of gas concentration measuring instruments are needed to achieve synchronous high-frequency measurement of the concentrations of multiple gas components, such as a time-of-flight mass spectrometer for measuring the high-frequency concentration of volatile organic compounds and a tunable infrared laser direct absorption spectrometer for measuring the high-frequency concentration of carbon monoxide. Due to the weight and volume limitations of these gas concentration measuring instruments, as well as the needs of maintenance and power supply, it is impossible to place many gas concentration measuring instruments on a high tower at the same time according to the existing flux measurement method. They can only be placed in a ground station, resulting in serious misalignment of the high-altitude sampling ports and multiple gas concentration measuring instruments in space. The existing flux measurement method suitable for vegetation ecosystems is difficult to effectively solve the problem of spatial misalignment, which causes the gas concentration measuring instruments located on the ground to be unable to sample high-altitude air, unable to simultaneously determine the concentrations of multiple components, and the inconsistent time axis of high-altitude wind speed and ground concentration, and is unable to support the flux measurement of multiple gas components in urban areas. Summary of the invention

[0005] The purpose of this application is to provide a multi-component flux measurement system and method for urban areas based on the eddy covariance method, which can carry out flux measurement of multiple gas components in urban areas.

[0006] To achieve the above objectives, this application provides the following solutions.

[0007] In a first aspect, the present application provides a system for measuring multi-component flux in urban areas based on an eddy covariance method, wherein the system for measuring multi-component flux in urban areas based on an eddy covariance method comprises:

[0008] Multi-satellite clock synchronization timing module is used to synchronize the timing of the high-altitude micrometeorological measurement module and each ground multi-component concentration measurement module;

[0009] The high-altitude micro-meteorological measurement module is installed on a high-altitude observation platform in an urban area and is connected to the multi-satellite clock synchronization timing module for communication, and is used to measure the vertical wind speed at the high-altitude observation platform at a preset frequency during the observation period to obtain a vertical wind speed time series; the high-altitude observation platform is in a constant flux layer;

[0010] An ex situ sample transmission module is used to collect air at a high-altitude observation platform and transmit the air in a turbulent state to a ground multi-component concentration measurement module corresponding to each component to be measured; the component to be measured is a gas component in the air;

[0011] A ground multi-component concentration measurement module is located on the ground and is connected to the multi-satellite clock synchronization timing module for communication, and is used to measure the concentration of the component to be measured in the air at a preset frequency during an observation period to obtain a concentration time series corresponding to the component to be measured;

[0012] The cumulative covariance time lag determination module is respectively connected to the high-altitude micrometeorological measurement module and the ground multi-component concentration measurement module for calculating the time lag corresponding to the component to be measured for each component to be measured based on the vertical wind speed time series and the concentration time series corresponding to the component to be measured;

[0013] The multi-component flux calculation module is communicatively connected to the cumulative covariance time lag determination module, and is used to calculate the flux corresponding to the component to be measured for each component to be measured based on the vertical wind speed time series, the concentration time series corresponding to the component to be measured and the time lag corresponding to the component to be measured.

[0014] In a second aspect, the present application provides a method for measuring multi-component flux in urban areas based on the eddy covariance method, which is applied to the above-mentioned multi-component flux measurement system in urban areas based on the eddy covariance method. The multi-component flux measurement method in urban areas based on the eddy covariance method includes:

[0015] Obtain the vertical wind speed time series and the concentration time series corresponding to each component to be measured during the observation period;

[0016] For each of the components to be tested, perform the following steps:

[0017] Dividing the observation period into a plurality of unit times;

[0018] For each unit time, determine the vertical wind speed sub-time series and the concentration sub-time series corresponding to the component to be measured within the unit time; calculate the covariance sequence corresponding to the unit time based on the vertical wind speed sub-time series and the concentration sub-time series; the covariance sequence includes covariances corresponding to different time lags;

[0019] Adding the covariance sequences corresponding to all the unit times to obtain a summed covariance sequence, and selecting the time lag corresponding to the maximum value of the summed covariance sequence as the time lag corresponding to the component to be measured;

[0020] Based on the vertical wind speed time series, the concentration time series corresponding to the component to be measured and the time lag corresponding to the component to be measured, the flux corresponding to the component to be measured is calculated.

[0021] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0022] The present application provides a system and method for measuring multi-component flux in urban areas based on the eddy covariance method, wherein a multi-satellite clock synchronization timing module is set to synchronize the timing of the high-altitude micrometeorological measurement module and each ground multi-component concentration measurement module; the high-altitude micrometeorological measurement module is set to measure the vertical wind speed at the high-altitude observation platform at a preset frequency during the observation period to obtain a vertical wind speed time series; an off-site sample transmission module is set to collect air at the high-altitude observation platform, and transmit the air in a turbulent state to the ground multi-component concentration measurement module corresponding to each component to be measured; the ground multi-component concentration measurement module is set to measure the vertical wind speed at a preset frequency in the air during the observation period. The concentration of the component is measured to obtain the concentration time series corresponding to the component to be measured; a cumulative covariance time lag determination module is set to calculate the time lag corresponding to the component to be measured for each component to be measured based on the vertical wind speed time series and the concentration time series corresponding to the component to be measured; a multi-component flux calculation module is set to calculate the flux corresponding to the component to be measured for each component to be measured based on the vertical wind speed time series, the concentration time series corresponding to the component to be measured and the time lag corresponding to the component to be measured. This solves the problem that the existing flux measurement method suitable for vegetation ecosystems is difficult to effectively solve a series of problems caused by spatial heterogeneity, and flux measurements of multiple gas components can be carried out in urban areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A schematic diagram of the structure of a multi-component flux measurement system for urban areas based on the eddy covariance method provided in Example 1 of the present application.

[0025] Figure 2 This is a schematic diagram of the structure of the metal bracket provided in Example 1 of the present application.

[0026] Figure 3 This is a schematic diagram of the structure of the high-altitude sampling module provided in Example 1 of the present application.

[0027] Figure 4 This is a schematic diagram of the structure of the ground pipeline diversion module provided in Example 1 of the present application.

[0028] Reference numerals:

[0029] 1-mounting rod; 2-first metal rod; 3-second metal rod; 4-three-dimensional ultrasonic anemometer; 5-high altitude sampling module; 6-three-way connector; 7-diversion pipeline. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] Example 1.

[0032] like Figure 1 As shown, this embodiment provides an urban area multi-component flux measurement system based on the eddy covariance method, and the urban area multi-component flux measurement system based on the eddy covariance method includes the following components.

[0033] The multi-satellite clock synchronization timing module is used to synchronize the timing of the high-altitude micrometeorological measurement module and each ground multi-component concentration measurement module.

[0034] The high-altitude micrometeorological measurement module is installed on the high-altitude observation platform in the urban area and is connected to the multi-satellite clock synchronization timing module. It is used to measure the vertical wind speed at the high-altitude observation platform at a preset frequency during the observation period to obtain the vertical wind speed time series. The high-altitude observation platform is in a constant flux layer.

[0035] The ex situ sample transmission module is used to collect air at the high-altitude observation platform and transmit the air in a turbulent state to the ground multi-component concentration measurement module corresponding to each component to be measured. The components to be measured are the gas components in the air.

[0036] The ground multi-component concentration measurement module is located on the ground and is connected to the multi-satellite clock synchronization timing module for communication. It is used to measure the concentration of the component to be measured in the air at a preset frequency during the observation period to obtain the concentration time series corresponding to the component to be measured.

[0037] The cumulative covariance time lag determination module is respectively connected to the high-altitude micrometeorological measurement module and the ground multi-component concentration measurement module for communicating with each other, and is used to calculate the time lag corresponding to the component to be measured for each component to be measured based on the vertical wind speed time series and the concentration time series corresponding to the component to be measured.

[0038] The multi-component flux calculation module is communicated with the cumulative covariance time lag determination module and is used to calculate the flux corresponding to the component to be measured for each component to be measured based on the vertical wind speed time series, the concentration time series corresponding to the component to be measured and the time lag corresponding to the component to be measured.

[0039] This embodiment proposes a multi-component flux measurement system for urban areas based on the eddy covariance method, which is a method for measuring the flux of ecological environmental materials. It aims to specifically solve the problem of the spatial dislocation of high-altitude sampling ports and multiple gas concentration measurement instruments during current urban flux measurements, construct a multi-component flux measurement system suitable for urban areas, supplement the current technical constraints and methodological deficiencies, and solve the problem that the existing flux measurement method based on the eddy covariance method cannot carry out flux measurements of multiple gas components in complex urban underlying surfaces.

[0040] Among them, the preset frequency is generally 10 Hz. At this time, the vertical wind speed time series can be called a high-frequency vertical wind speed time series, and the concentration time series can be called a high-frequency concentration time series.

[0041] The problems caused by spatial dislocation involve dislocation sample transmission, turbulence state determination, pipeline wear, multi-instrument collaborative measurement, terminal low-pressure sampling, temperature difference condensation phenomenon, response change under variable pressure, multi-instrument time synchronization, long time lag determination and multi-component flux calculation method. Therefore, considering the impact of building height in urban areas on multi-component flux measurement, this embodiment, on the basis of the existing flux measurement method based on eddy covariance method, adopts a series of technical means and methodological innovations such as long pipeline large flow sample transmission, turbulence determination inspection, casing protection, pipeline diversion, auxiliary sampling, pipeline insulation, variable pressure multi-point calibration, multi-satellite timing, optimized time lag determination and specific flux calculation to construct a multi-component flux measurement system suitable for urban areas.

[0042] The following, combined Figure 1 The structure of the urban area multi-component flux measurement system of this embodiment is introduced in detail.

[0043] 1. High-altitude micrometeorological measurement module.

[0044] The high-altitude micrometeorological measurement module is installed on high-altitude observation platforms in urban areas, such as high-altitude observation platforms on high towers. It includes a high-frequency wind speed measurement module, a high-frequency data acquisition module and a power control module, which provide high-frequency measurement and recording of micrometeorological data (i.e. vertical wind speed) for the determination of multi-component fluxes.

[0045] The high-altitude observation platform is located in the constant flux layer, which refers to the area at the bottom of the atmospheric boundary layer near the near-ground layer where the flux of matter and energy does not change with altitude. The lowest altitude of the constant flux layer is generally 2-3 times higher than the ecosystem vegetation canopy height or the average building height.

[0046] (1) High-frequency wind speed measurement module.

[0047] The high-frequency wind speed measurement module is installed on the high-altitude observation platform in the urban area and is used to measure the vertical wind speed at the high-altitude observation platform at a preset frequency during the observation period.

[0048] like Figure 2 As shown, the high-frequency wind speed measurement module includes: a metal bracket and a three-dimensional ultrasonic anemometer 4. The metal bracket is installed on a high-altitude observation platform in an urban area, and the three-dimensional ultrasonic anemometer 4 is installed on the metal bracket.

[0049] The three-dimensional ultrasonic anemometer 4 can use ultrasonic technology to measure the wind speed and direction information in three dimensions, namely, horizontal, longitudinal and vertical directions. In order to meet the requirements of the flux measurement method, it must have a high-frequency measurement capability of 10 Hz, that is, measure and record 10 times per second.

[0050] The metal bracket can stably fix the three-dimensional ultrasonic anemometer 4 on the arm of the high-altitude observation platform of the tower. The arm is set horizontally. The metal bracket can be made of but not limited to stainless steel, aluminum alloy and other materials. The metal bracket specifically includes two metal rods at 90 degrees to each other. The metal rods can be made of but not limited to round tubes, square tubes and triangular tubes. The fixing methods of the two metal rods can be selected from permanent fixing and adjustable fixing. The permanent fixing method includes but is not limited to flange connection and welding, etc., and the adjustable fixing method includes but is not limited to clamps, screw sleeves, etc. The first metal rod is fixed vertically to the tower arm, and the fixing angle is at a certain angle to the horizontal plane, generally 45 degrees. The fixing method includes but is not limited to annular clamps, flange connections, welding, etc. The second metal rod is parallel to the tower arm and points in the same direction as the tower arm. The three-dimensional ultrasonic anemometer 4 is fixed to the end of the second metal rod, and the fixing method includes but is not limited to screw sleeves, flange connections, welding, etc. The length of the two metal rods can be flexibly adjusted according to the load-bearing requirements, and the shortest is generally not less than 40cm. The design of the metal bracket can prevent the three-dimensional ultrasonic anemometer 4 from being located in the same horizontal plane and the same vertical plane as the tower arm, thereby ensuring the measurement accuracy of the horizontal wind speed and the vertical wind speed to the greatest extent.

[0051] In this embodiment, the metal bracket includes a first metal rod 2 and a second metal rod 3. The first metal rod 2 is installed on a horizontally arranged mounting rod 1 (which can be an extension arm) on a high-altitude observation platform in an urban area. The first metal rod 2 is perpendicular to the mounting rod 1, and the first metal rod 2 is at a preset angle to the horizontal plane. The second metal rod 3 is installed on the first metal rod 2, the second metal rod 3 is perpendicular to the first metal rod 2, and the second metal rod 3 is parallel to the mounting rod 1. The three-dimensional ultrasonic anemometer 4 is installed at the end of the second metal rod 3.

[0052] (2) High-frequency data acquisition module.

[0053] The high-frequency data acquisition module is installed on the high-altitude observation platform in the urban area and is connected to the high-frequency wind speed measurement module for adding time information to the vertical wind speed and storing the vertical wind speed with time information to obtain the vertical wind speed time series.

[0054] The high-frequency data acquisition module is a device for recording high-frequency data. In order to meet the requirements of the flux measurement method, it must have the ability to record high-frequency data at 10 Hz. The high-frequency data acquisition module is connected to the three-dimensional ultrasonic anemometer 4. The high-frequency digital signal output by the three-dimensional ultrasonic anemometer 4 is transmitted to the high-frequency data acquisition module through a signal line. The high-frequency data acquisition module can add time information to the high-frequency digital signal and store the high-frequency digital signal in a user-defined format.

[0055] (3) Power control module.

[0056] The power control module is installed on the high-altitude observation platform in the urban area, and is electrically connected to the high-frequency wind speed measurement module and the high-frequency data acquisition module respectively, and is used to supply power to the high-frequency wind speed measurement module and the high-frequency data acquisition module.

[0057] The power control module includes an air switch module, a lightning protection module and a DC power transformer. The air switch module, the lightning protection module and the DC power transformer are connected in sequence to provide DC power for the high-frequency wind speed measurement module and the high-frequency data acquisition module. The air switch module is installed in the circuit. When the current exceeds the rated current, it can be automatically disconnected to prevent damage to the equipment (i.e., the high-frequency wind speed measurement module and the high-frequency data acquisition module) when short circuits, severe overloads and undervoltages occur. The lightning protection module can prevent lightning and other internal excessive voltages from invading the equipment and causing damage to the equipment. The DC power transformer can convert the input 220V AC power into DC output. The output power and DC output voltage can be adjusted according to actual conditions.

[0058] (ii) Ex situ sample transfer module.

[0059] The ex situ sample transmission module includes a high-altitude sampling module, a large-aperture sample transmission module, a ground pipeline diversion module, a large-flow drainage module and a turbulence determination module.

[0060] (1) High-altitude sampling module.

[0061] The high-altitude sampling module is installed on the high-altitude observation platform in the urban area. It is located behind the high-altitude micrometeorological measurement module and is within a preset distance from the high-altitude micrometeorological measurement module. It is used to collect air at the high-altitude observation platform.

[0062] like Figure 3 As shown, the high-altitude sampling module 5 of this embodiment is an inverted funnel-shaped sample inlet, the upper end of which is connected to the sample transmission pipeline in the large-aperture sample transmission module, and the lower end is open. The air sample enters the high-altitude sampling module 5 from the lower end and further enters the sample transmission pipeline to prevent water droplets from entering the sampling pipeline during precipitation and affecting the measurement results. The high-altitude sampling module 5 is fixed to the rear side of the three-dimensional ultrasonic anemometer 4. The wind direction is defined as rearward in this embodiment. At this time, the wind first passes through the three-dimensional ultrasonic anemometer 4 and then passes through the high-altitude sampling module 5. There is a difference between the position of the high-altitude sampling module 5 and the position of the three-dimensional ultrasonic anemometer 4, which is generally within 10-20 cm.

[0063] (2) Large aperture sample transmission module.

[0064] The large-aperture sample transmission module is connected to the high-altitude sampling module 5 at one end and to the ground pipeline diversion module at the other end, and is used to transmit air to the ground pipeline diversion module, that is, it can transmit the air from the high-altitude sampling site to the ground observation site.

[0065] The large-aperture sample transmission module includes: a sample transmission pipeline and a protective sleeve. One end of the sample transmission pipeline is connected to the high-altitude sampling module 5, and the other end of the sample transmission pipeline is connected to the ground pipeline diversion module. The protective sleeve wraps the sample transmission pipeline, and the protective sleeve is used to protect the sample transmission pipeline.

[0066] The outer diameter of the sample transmission pipeline is not less than 1 / 2 inch, and its material can be Teflon. Its length can be adjusted according to actual conditions. It is installed and fixed based on the high tower structure, one end is connected to the high-altitude sampling module 5, and the other end is connected to the ground pipeline diversion module. The purpose is to transmit air from the high-altitude sampling port to the ground.

[0067] The protective sleeve is a corrugated open sleeve, which can be made of PE plastic or PP material, with a longitudinal opening and a diameter of generally 1 inch. Its length can be adjusted according to the length of the sample transmission pipeline. The sample transmission pipeline can be inserted section by section through the longitudinal opening, which can effectively prevent the contact surface wear between the sample transmission pipeline and the tower caused by long-term vibration, and can also prevent pipeline damage caused by rodents.

[0068] (3) Ground pipeline diversion module.

[0069] The ground pipeline diversion module is connected to the ground multi-component concentration measurement module corresponding to each component to be measured, and is used to transmit the air to the ground multi-component concentration measurement module corresponding to each component to be measured, that is, it can divert the air transmitted to the ground by the sample transmission pipeline to each ground multi-component concentration measurement module.

[0070] like Figure 4 As shown, the ground pipeline diversion module includes: a plurality of three-way joints 6 connected in sequence, the first three-way joint 6 is connected to the sample transmission pipeline, two adjacent three-way joints 6 are connected via a diversion pipeline 7, the three-way joints 6 correspond one to one with the ground multi-component concentration measurement module, and each three-way joint 6 is connected to the ground multi-component concentration measurement module.

[0071] The three-way connector 6 can be made of Teflon material and its size can be 1 / 2 inch. Its number is the same as the number of ground multi-component concentration measurement modules and corresponds one-to-one with the ground multi-component concentration measurement modules. The air transmitted from high altitude is distributed to each ground multi-component concentration measurement module with the help of the vertical interface of the three-way connector 6.

[0072] The shunt pipe 7 can be made of Teflon material, and its outer diameter can be 1 / 2 inch. It is used to connect multiple three-way connectors 6, and its length can be flexibly adjusted according to the position of the three-way connectors 6.

[0073] In this embodiment, the ground pipeline diversion module also includes: a one-way valve group and a pipeline insulation unit.

[0074] The one-way valve group includes multiple first one-way valves, the number of which is the same as the number of ground multi-component concentration measurement modules, and corresponds one-to-one to the ground multi-component concentration measurement modules. The first one-way valve is installed on the connecting pipeline used to connect the three-way joint 6 and the ground multi-component concentration measurement module. Specifically, it can be connected to the vertical interface of the three-way joint 6, and is installed between the three-way joint 6 and the sampling air inlet end of the component concentration high-frequency measuring instrument in the ground multi-component concentration measurement module. It can control the one-way flow of air in the pipeline to prevent the component concentration high-frequency measuring instrument from having insufficient sampling suction, resulting in back suction, and sucking the ground air back into the diversion pipeline 7 to cause pollution. At the same time, it can also avoid damaging the sealing of the component concentration high-frequency measuring instrument.

[0075] The pipeline insulation unit includes an insulation sleeve, a heating belt and a temperature control unit, which can prevent the condensation of water vapor caused by the temperature difference between the sample transmission pipeline and the shunt pipeline 7, avoid the generation of liquid water, cause pipeline blockage and damage the component concentration high-frequency measuring instrument. The insulation sleeve wraps each shunt pipeline 7, the heating belt is located between the insulation sleeve and the shunt pipeline 7, and the temperature control unit is used to measure the temperature of the heating belt and control the heating process of the heating belt based on the temperature.

[0076] The insulation sleeve can be a high-density rubber-plastic insulation pipe with an inner diameter of 1 inch and a longitudinal opening. Its length can be adjusted according to the length of the shunt pipe 7. The shunt pipe 7 can be inserted through the longitudinal opening, and it has the function of heat preservation and flame retardancy.

[0077] The heating belt can be a plug-type flame-retardant heating belt, and its length can be adjusted according to the length of the shunt pipeline 7. The heating belt and the shunt pipeline 7 are sheathed together through an insulation sleeve to provide a pipeline heating function.

[0078] The temperature control unit consists of a temperature probe and a thermostat. The temperature probe can measure the temperature of the heating belt. The thermostat can set the temperature control range of the heating belt and control the power supply of the heating belt. When the temperature of the heating belt reaches the lower limit of the temperature control range, the thermostat supplies power to the heating belt and starts heating; when the temperature of the heating belt reaches the upper limit of the temperature control range, the thermostat cuts off the power to the heating belt and stops heating.

[0079] (4) Large flow diversion module.

[0080] The large-flow drainage module is connected to the ground pipeline diversion module to speed up the transmission of air in the large-aperture sample transmission module and the ground pipeline diversion module, that is, it can provide sufficient vacuum at the end of the pipeline to quickly transmit air from the high-altitude sampling site to the ground observation site through the sample transmission pipeline.

[0081] The large flow drainage module comprises: a vacuum pump, which is connected to the last three-way connector 6.

[0082] The vacuum pump can be a large-flow vacuum pump, which is a high-power rotary vane vacuum pump that can provide a large flow. Its rated power and maximum suction flow can be flexibly selected according to the height of the high-altitude sampling port and the length of the sample transmission pipeline. It is connected to the diversion pipeline 7 on the ground to provide a large amount of suction flow, and quickly transmit the air from the high-altitude sampling port to the ground through the sample transmission pipeline.

[0083] In this embodiment, the large flow drainage module further includes: a flow limiting orifice plate and a second one-way valve. The flow limiting orifice plate is installed on the shunt pipeline 7 located before the vacuum pump. The second one-way valve is installed on the shunt pipeline 7 located between the vacuum pump and the flow limiting orifice plate.

[0084] The flow limiting orifice plate can be made of stainless steel and installed upstream of the large flow vacuum pump in the pipeline to play a role in stabilizing the flow. The flow limiting aperture can be flexibly adjusted according to demand, generally 1 / 4 inch.

[0085] The second one-way valve can be a one-way closing valve with a 1 / 2-inch interface. It is installed between the large-flow vacuum pump and the limiting orifice plate, allowing the airflow to flow in one direction only. It is closed when the airflow flows in the reverse direction, which can prevent the large-flow vacuum pump from generating reverse gas flow during operation, thereby ensuring the working efficiency and safety of the large-flow vacuum pump.

[0086] (5) Turbulence determination module.

[0087] The turbulence determination module is used to detect the average flow velocity of the air in the large-aperture sample transmission module, calculate the Reynolds number based on the average flow velocity and the inner diameter of the pipeline in the large-aperture sample transmission module, and determine whether the air in the large-aperture sample transmission module is in a turbulent state based on the Reynolds number.

[0088] The Reynolds number is a dimensionless number that can be used to characterize the flow conditions of a fluid. It is calculated based on the flow velocity, density, viscosity coefficient and pipe size of the fluid. Flows with a Reynolds number less than 2300 are laminar flows, flows with a Reynolds number between 2300 and 4000 are transitional flows, and flows with a Reynolds number greater than 4000 are turbulent flows.

[0089] The turbulence determination module is a method for determining the state of the fluid in the sample transmission pipeline. It introduces the Reynolds number representing the state of the pipeline fluid, determines the air density, air viscosity coefficient, and inner diameter of the sample transmission pipeline, and measures the average flow rate of the air in the sample transmission pipeline, calculates the Reynolds number of the air in the sample transmission pipeline, and determines the turbulent state in the pipeline based on the obtained Reynolds number. When the Reynolds number result is greater than 4000, it can be determined that the gas transmission in the sample transmission pipeline is turbulent, that is, the high-altitude air still retains the information of turbulent pulsation after long-distance pipeline transmission, which meets the turbulent transmission theory assumption of flux measurement, thereby verifying the fidelity of the turbulent pulsation information during the sample transmission process and ensuring that the theoretical assumptions are met. If the theoretical assumptions are not met, the designed system needs to be adjusted until the theoretical assumptions are met.

[0090] (3) Ground multi-component concentration measurement module.

[0091] The ground multi-component concentration measurement module includes: a component concentration measurement module, a low-pressure auxiliary drainage sampling module and a variable pressure calibration module. It can collect air from the three-way joint 6 in the ground pipeline diversion module to carry out high-frequency concentration measurement, response calibration and data recording.

[0092] (1) Component concentration measurement module.

[0093] The component concentration measurement module includes: a component concentration high-frequency measurement instrument and a workstation, which can perform high-frequency concentration measurement and data recording for certain components and some components in the air. The component concentration high-frequency measurement instrument is used to measure the concentration of the component to be measured in the air at a preset frequency during the observation period. The workstation is connected to the component concentration high-frequency measurement instrument for communication. The workstation is used to add time information to the concentration and store the concentration with time information to obtain the concentration time series corresponding to the component to be measured.

[0094] Applications of high-frequency component concentration measurement instruments include but are not limited to online mass spectrometry technology, cavity-enhanced absorption spectroscopy technology and other technologies. They can perform high-frequency measurements on a certain component or certain components at the same time, and the measurement frequency is generally 10 Hz.

[0095] The workstation includes but is not limited to desktop computers, laptop computers and server workstations, which are connected to the component concentration high-frequency measuring instrument through a signal transmission line, and the operating system includes but is not limited to Windows, IOS and Linux.

[0096] (2) Low-pressure auxiliary drainage sampling module.

[0097] The ground shunt pipe 7 is located at the end of the sample transmission pipeline. A large pressure drop is formed at the end of the large-flow and long-distance pipeline. Due to the pressure drop at the end, the air pressure in the shunt pipe 7 and at the three-way joint 6 is extremely low, which may reach below 0.5 atmospheres. As a result, the high-frequency component concentration measuring instrument designed for atmospheric pressure sampling is difficult to collect air in the low-pressure pipeline. The low-pressure auxiliary drainage sampling module can provide additional sampling flow to assist the high-frequency component concentration measuring instrument to collect the air to be analyzed from the ground shunt pipe 7.

[0098] The low-pressure auxiliary drainage sampling module comprises: an auxiliary sampling pipeline and a low-pressure auxiliary drainage pump, which are connected to the sampling outlet end of the component concentration high-frequency measuring instrument.

[0099] The auxiliary sampling pipeline can be a Teflon material pipeline, the length and diameter of which are determined according to actual needs, and is used to connect the sampling outlet end of the component concentration high-frequency measuring instrument and the low-pressure auxiliary drainage pump.

[0100] The low-pressure auxiliary drainage pump may include but is not limited to a diaphragm vacuum pump, a rotary vane vacuum pump and a piston vacuum pump. Its rated power and sampling flow rate can be determined according to actual needs. It is installed at the sampling outlet of the component concentration high-frequency measuring instrument to provide additional sampling flow rate to assist the sampling process of the component concentration high-frequency measuring instrument.

[0101] (3) Transformer calibration module.

[0102] The variable pressure calibration module is used to perform variable pressure calibration on high-frequency component concentration measuring instruments. It can simulate pipeline pressures of different gradients and provide a low-pressure sampling environment and standard gases of different concentrations for variable pressure multi-point calibration of high-frequency component concentration measuring instruments.

[0103] The variable pressure calibration module includes: a calibration pipeline, a pipeline pressure control unit and a standard gas dilution unit. The air inlet of the calibration pipeline is connected to the standard gas dilution unit, the first air outlet of the calibration pipeline is connected to the pipeline pressure control unit, and the second air outlet of the calibration pipeline is connected to the sampling air inlet of the component concentration high-frequency measuring instrument. The pipeline pressure control unit is used to control the pressure in the calibration pipeline. The standard gas dilution unit is used to provide preset diluted standard gases of different concentrations.

[0104] The pipeline pressure control unit is an upstream pressure controller. The preset pressure adjustment range includes but is not limited to 0.3 to 1 atmosphere. It can adjust the outlet flow of the calibration pipeline based on the preset calibration pipeline pressure and the gas supply flow in the calibration pipeline to achieve the purpose of controlling the pressure in the calibration pipeline.

[0105] The standard gas dilution unit consists of a standard gas source and a dilution ratio component. The standard gas source is a standard gas of known concentration (i.e., standard gas, which can be selected as needed). The dilution ratio component can adjust the dilution ratio. By calculating and setting the dilution ratio in the dilution ratio component, the preset diluted standard gas of different concentrations can be obtained.

[0106] This embodiment utilizes the pressure control capability of the pipeline pressure control unit on the upstream pipeline to provide an adjustable pipeline pressure environment. Combined with the multi-concentration mixed standard gas provided by the standard gas dilution unit, it can provide a multi-concentration calibration environment under variable pressure conditions for the component concentration high-frequency measuring instrument, and provide technical support for calibrating the instrument response concentration curve under different pipeline pressure conditions.

[0107] (IV) Multi-satellite clock synchronization timing module.

[0108] The multi-satellite clock synchronization timing module includes a satellite timing module and a time synchronization module. By using the timing function provided by satellite signals, it can provide synchronous timing for the high-altitude micrometeorological measurement module and the ground multi-component concentration measurement module based on multiple earth orbit satellite signals to ensure the accuracy of timing. The satellite timing module can receive signals from multiple earth orbit satellites to achieve synchronous timing. The time synchronization module can establish a local area network and provide the synchronous timing function of the NTP protocol (Network Time Protocol) as a client. The NTP protocol is a protocol used to synchronize computer time. It can synchronize the computer with its timing server and provide high-precision time correction.

[0109] In this embodiment, the multi-satellite clock synchronization timing module includes the following components.

[0110] The first satellite timing module is installed on the high-altitude observation platform in the urban area and is connected to the port of the high-frequency data acquisition module of the high-altitude micrometeorological measurement module through a signal line. It is used to provide time for the high-altitude micrometeorological measurement module, that is, to provide timing operations when the high-frequency data acquisition module is recording high-frequency data.

[0111] The second satellite timing module is located on the ground and is used to provide timing for the time synchronization module.

[0112] The time synchronization module is located on the ground and is connected to the second satellite timing module for providing timing for each ground multi-component concentration measurement module.

[0113] The second satellite timing module and the time synchronization module jointly provide time synchronization operations for ground instruments. The second satellite timing module is connected to the time synchronization module via a network cable. The workstation of each component concentration measurement module in the ground multi-component concentration measurement module is connected to the local timing network established by the time synchronization module, and a timing application is sent to the client regularly through the NTP protocol. The protocol supports multiple instrument workstation operating systems including Windows, IOS and Linux, and realizes the synchronous timing of multiple ground multi-component concentration measurement module data records, which is generally completed every half an hour.

[0114] The satellite timing module of this embodiment is respectively applied to the high-frequency data acquisition module in the high-altitude micrometeorological measurement module and the workstation in the component concentration measurement module in the ground multi-component concentration measurement module. Through the regular time correction with multiple earth orbit satellite signals, it ensures that the high-frequency data records at high altitude and on the ground share the satellite clock, so as to achieve the time axis unification between the off-site observations. The time synchronization module builds a local timing network based on the NTP protocol, which can support multiple operating systems including Windows, IOS and Linux, and supports the synchronization of workstations of multiple component concentration measurement modules, ensuring the time axis unification when the ground station instruments are used together to carry out multi-component synchronous high-frequency determination.

[0115] (V) Cumulative covariance lag determination module.

[0116] The cumulative covariance time lag determination module is respectively connected to the high-altitude micrometeorological measurement module and the ground multi-component concentration measurement module for communicating with each other, and is used to calculate the time lag corresponding to the component to be measured for each component to be measured based on the vertical wind speed time series and the concentration time series corresponding to the component to be measured.

[0117] When conducting flux measurements, due to differences in the locations of concentration and vertical wind speed sampling points and electronic equipment response delays, the concentration measuring instrument has a time lag (i.e., time lag) in data measurement compared to the wind speed measuring instrument. In the existing flux measurement method, the maximum covariance method is applied to make a time lag determination every half an hour. The covariance of the concentration pulsation term and the wind speed pulsation term after the shift is calculated by shifting the concentration time axis to the left and right in units of 0.1 seconds within the preset time window, and the shift time when the covariance is the largest is taken as the time lag, that is, the covariance sequence of the wind speed pulsation and the concentration pulsation at different shift times is calculated. The shift time corresponding to the peak of the covariance sequence is determined as the time lag and included in the subsequent flux calculation.

[0118] However, the above method has the defect of inaccuracy. In order to solve this problem, the cumulative covariance time lag determination module of the present embodiment calculates the covariance sequence of the vertical wind speed pulsation and the concentration pulsation of a certain component to be measured every half hour, superimposes the covariance sequences of all half hours in the observation period, amplifies the covariance peak corresponding to the best offset time, and determines the offset time corresponding to the peak of the superimposed covariance sequence as the time lag corresponding to the component to be measured. This method is more accurate for time lag determination of periods with lower flux and components with lower flux.

[0119] Specifically, for each component to be measured, the following steps are performed: the observation period is divided into a plurality of unit times; for each unit time, the vertical wind speed sub-time series within the unit time and the concentration sub-time series corresponding to the component to be measured are determined; based on the vertical wind speed sub-time series and the concentration sub-time series, the covariance sequence corresponding to the unit time is calculated, and the covariance sequence includes covariances corresponding to different time lags; the covariance sequences corresponding to all unit times are added to obtain the added covariance sequence, and the time lag corresponding to the maximum value of the added covariance sequence is selected as the time lag corresponding to the component to be measured.

[0120] The cumulative covariance time-lag determination module of this embodiment accumulates the covariance sequences of all half hours within the observation time, highlights and amplifies the covariance peak value corresponding to the optimal misalignment time, thereby completing the time-lag determination and improving the flux measurement accuracy of the low-flux gas component.

[0121] (vi) Multi-component flux calculation module.

[0122] The multi-component flux calculation module is communicated with the cumulative covariance time lag determination module and is used to calculate the flux corresponding to the component to be measured for each component to be measured based on the vertical wind speed time series, the concentration time series corresponding to the component to be measured and the time lag corresponding to the component to be measured.

[0123] The multi-component flux calculation module is a flux calculation method based on specific time lag for each component to be measured. The specific method is that for each component to be measured, the result of the cumulative covariance time lag judgment module is used as the specific time lag, so as to move the time axis of the high-frequency concentration pulsation to achieve a one-to-one correspondence with the high-frequency vertical wind speed pulsation, calculate the covariance of the two, and obtain the flux result of the corresponding component to be measured.

[0124] The multi-component flux calculation module of this embodiment adopts a component-specific calculation method, performs independent time-lag judgment on different components, obtains specific time-lag data, and obtains flux results based on this calculation. It can better adapt to the phenomenon of inconsistent data recording delays caused by differences in component measurement principles of multiple concentration measuring instruments, and improve the accuracy of multi-component flux calculation.

[0125] The multi-component flux measurement system for urban areas based on the eddy covariance method provided in this embodiment includes an upper air micrometeorological measurement module, an off-site sample transmission module, a ground multi-component concentration measurement module, a multi-satellite clock synchronization timing module, a cumulative covariance time lag determination module, and a multi-component flux calculation module. The wind speed observation instrument and the concentration measurement instrument are placed off-site, respectively at the upper air sampling site and the ground observation site, and a large-caliber pipeline and a large-flow vacuum pump are used to realize the rapid transmission of air from the upper air sampling site to the ground observation site. In the measurement of multi-gas component flux in urban areas, the biggest disadvantage of the existing flux measurement method is that it cannot properly deal with the technical constraints and methodological deficiencies caused by the spatial off-site measurement of wind speed and multi-gas concentration. This embodiment adopts a series of technical means and methodological innovations such as long pipeline large-flow sample transmission, turbulence determination inspection, casing protection, pipeline diversion, auxiliary sampling, variable pressure multi-point calibration, pipeline insulation, multi-satellite timing, optimized time lag determination and specific flux calculation, which effectively solves the above problems. Large-diameter pipelines and large-flow vacuum pumps are used to carry air between high-altitude sampling sites and ground concentration measuring instruments, thereby greatly shortening the air transmission time in the pipeline. Reynolds number determination is introduced for the fluid state of the transmission pipeline, so that the fidelity of turbulence information can be verified to ensure that the assumptions of the theory are met. Casing protection is applied to prevent wear caused by long-term vibration of long-distance pipelines and tower structures. Pipeline diversion is used to achieve system measurement of multiple instruments. With the help of auxiliary sampling skills, the sampling of high-frequency component concentration measuring instruments in the terminal low-pressure pipeline is assisted. Variable-pressure multi-point calibration is established to provide a multi-concentration calibration environment under variable pressure for high-frequency component concentration measuring instruments, so as to obtain instrument response concentration curves under different pipeline pressure conditions. Pipeline insulation technology is used to prevent water vapor condensation caused by the temperature difference between the sample transmission pipeline and the diversion pipeline 7, avoid the generation of liquid water, cause pipeline blockage and damage the high-frequency component concentration measuring instrument. The clock synchronization capability of multiple satellites is used to synchronize the timing of different instruments in different spatial locations to ensure the uniformity of the time axis of high-frequency data recording between different instruments. In order to solve the time lag judgment problem caused by long-distance transmission of samples, the cumulative covariance method is introduced to complete the specific component time lag judgment. The time lag covariance sequence of a single time window is accumulated and judged, and the covariance peak corresponding to the optimal misalignment time is amplified, which greatly improves the flux measurement accuracy of low-flux gas components. In summary, from the perspectives of technical means and methodology, this embodiment properly solves a series of problems currently caused by the spatial dislocation of high-altitude sampling ports and multi-gas concentration high-frequency measurement instruments, including dislocation sample transmission, turbulent state judgment, pipeline wear, multi-instrument collaborative measurement, terminal low-pressure sampling, temperature difference condensation phenomenon, response changes under variable pressure, multi-instrument time synchronization, long time lag judgment and multi-component flux calculation methods.

[0126] Example 2.

[0127] This embodiment provides a method for measuring multi-component flux in urban areas based on the eddy covariance method, which is applied to the multi-component flux measurement system in urban areas based on the eddy covariance method described in Example 1. The method for measuring multi-component flux in urban areas based on the eddy covariance method includes the following steps.

[0128] (1) Obtain the vertical wind speed time series and the concentration time series corresponding to each component to be measured during the observation period.

[0129] (2) For each component to be tested, perform the following steps.

[0130] (2.1) Divide the observation period into multiple unit times.

[0131] (2.2) For each unit time, determine the vertical wind speed sub-time series and the concentration sub-time series corresponding to the component to be measured within the unit time; based on the vertical wind speed sub-time series and the concentration sub-time series, calculate the covariance sequence corresponding to the unit time, and the covariance sequence includes the covariances corresponding to different time lags.

[0132] (2.3) The covariance sequences corresponding to all unit times are added to obtain the added covariance sequence, and the time lag corresponding to the maximum value of the added covariance sequence is selected as the time lag corresponding to the component to be measured.

[0133] (2.4) Based on the vertical wind speed time series, the concentration time series corresponding to the measured component and the time lag corresponding to the measured component, the flux corresponding to the measured component is calculated.

[0134] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A multi-component flux measurement system for urban areas based on eddy covariance method, characterized in that: The urban area multi-component flux measurement system based on the eddy covariance method includes: Multi-satellite clock synchronization timing module is used to synchronize the timing of the high-altitude micrometeorological measurement module and each ground multi-component concentration measurement module; The high-altitude micro-meteorological measurement module is installed on a high-altitude observation platform in an urban area and is connected to the multi-satellite clock synchronization timing module for communication, and is used to measure the vertical wind speed at the high-altitude observation platform at a preset frequency during the observation period to obtain a vertical wind speed time series; the high-altitude observation platform is in a constant flux layer; An ex situ sample transmission module is used to collect air at a high-altitude observation platform and transmit the air in a turbulent state to a ground multi-component concentration measurement module corresponding to each component to be measured; the component to be measured is a gas component in the air; A ground multi-component concentration measurement module is located on the ground and is connected to the multi-satellite clock synchronization timing module for communication, and is used to measure the concentration of the component to be measured in the air at a preset frequency during an observation period to obtain a concentration time series corresponding to the component to be measured; The cumulative covariance time lag determination module is respectively connected to the high-altitude micrometeorological measurement module and the ground multi-component concentration measurement module for calculating the time lag corresponding to the component to be measured for each component to be measured based on the vertical wind speed time series and the concentration time series corresponding to the component to be measured; The multi-component flux calculation module is communicatively connected to the cumulative covariance time lag determination module, and is used to calculate the flux corresponding to the component to be measured for each component to be measured based on the vertical wind speed time series, the concentration time series corresponding to the component to be measured and the time lag corresponding to the component to be measured.

2. The urban area multi-component flux measurement system based on the eddy covariance method according to claim 1, characterized in that: The multi-satellite clock synchronization timing module includes: The first satellite timing module is installed on the high-altitude observation platform in the urban area and is used to provide timing for the high-altitude micro-meteorological measurement module; The second satellite timing module is located on the ground and is used to provide timing for the time synchronization module; The time synchronization module is located on the ground and is connected to the second satellite timing module for providing timing for each ground multi-component concentration measurement module.

3. The urban area multi-component flux measurement system based on the eddy covariance method according to claim 1, characterized in that: The high-altitude micro-meteorological measurement module includes: A high-frequency wind speed measurement module is installed on a high-altitude observation platform in an urban area and is used to measure the vertical wind speed at the high-altitude observation platform at a preset frequency during the observation period; A high-frequency data acquisition module is installed on a high-altitude observation platform in an urban area and is in communication connection with the high-frequency wind speed measurement module, and is used to add time information to the vertical wind speed and store the vertical wind speed with time information to obtain a vertical wind speed time series; The power control module is installed on the high-altitude observation platform in the urban area, and is electrically connected to the high-frequency wind speed measurement module and the high-frequency data acquisition module respectively, and is used to supply power to the high-frequency wind speed measurement module and the high-frequency data acquisition module.

4. The urban area multi-component flux measurement system based on the eddy covariance method according to claim 3 is characterized in that: The high-frequency wind speed measurement module comprises: a metal bracket and a three-dimensional ultrasonic anemometer, wherein the metal bracket is installed on a high-altitude observation platform in an urban area, and the three-dimensional ultrasonic anemometer is installed on the metal bracket; Wherein, the metal bracket includes a first metal rod and a second metal rod; the first metal rod is installed on a horizontally arranged mounting rod on a high-altitude observation platform in an urban area, the first metal rod is perpendicular to the mounting rod, and the first metal rod is at a preset angle to the horizontal plane; the second metal rod is installed on the first metal rod, the second metal rod is perpendicular to the first metal rod, and the second metal rod is parallel to the mounting rod; the three-dimensional ultrasonic anemometer is installed at the end of the second metal rod.

5. The urban area multi-component flux measurement system based on the eddy covariance method according to claim 1, characterized in that: The ex situ sample transfer module includes: The high-altitude sampling module is installed on the high-altitude observation platform in the urban area, located behind the high-altitude micro-meteorological measurement module, and within a preset distance from the high-altitude micro-meteorological measurement module, and is used to collect air at the high-altitude observation platform; A large-aperture sample transmission module, one end of which is connected to the high-altitude sampling module, and the other end of which is connected to the ground pipeline diversion module, for transmitting the air to the ground pipeline diversion module; A ground pipeline shunt module is connected to a ground multi-component concentration measurement module corresponding to each component to be measured, and is used to transmit the air to the ground multi-component concentration measurement module corresponding to each component to be measured; A large flow drainage module is connected to the ground pipeline diversion module and is used to speed up the transmission speed of the air in the large-aperture sample transmission module and the ground pipeline diversion module; The turbulence determination module is used to detect the average flow velocity of the air in the large-aperture sample transmission module, calculate the Reynolds number based on the average flow velocity and the inner diameter of the pipeline in the large-aperture sample transmission module, and determine whether the air in the large-aperture sample transmission module is in a turbulent state based on the Reynolds number.

6. The urban area multi-component flux measurement system based on eddy covariance method according to claim 5, characterized in that: The large-aperture sample transmission module includes: a sample transmission pipeline and a protective sleeve; one end of the sample transmission pipeline is connected to the high-altitude sampling module, and the other end of the sample transmission pipeline is connected to the ground pipeline diversion module; the protective sleeve wraps the sample transmission pipeline, and the protective sleeve is used to protect the sample transmission pipeline; The ground pipeline shunt module includes: a plurality of three-way joints connected in sequence, the first three-way joint is connected to the sample transmission pipeline, two adjacent three-way joints are connected via a shunt pipeline, the three-way joints correspond to the ground multi-component concentration measurement modules one by one, and each of the three-way joints is connected to the ground multi-component concentration measurement module; The large flow drainage module comprises: a vacuum pump, and the vacuum pump is connected to the last three-way connector.

7. The urban area multi-component flux measurement system based on the eddy covariance method according to claim 6 is characterized in that: The ground pipeline diversion module also includes: a one-way valve group and a pipeline insulation unit; The one-way valve group includes a plurality of first one-way valves, each of the first one-way valves corresponds to a ground multi-component concentration measurement module, and the first one-way valve is installed on a connecting pipeline for connecting the three-way connector and the ground multi-component concentration measurement module; The pipeline insulation unit includes an insulation sleeve, a heating belt and a temperature control unit; the insulation sleeve wraps each of the shunt pipelines; the heating belt is located between the insulation sleeve and the shunt pipeline; the temperature control unit is used to measure the temperature of the heating belt and control the heating process of the heating belt based on the temperature.

8. The urban area multi-component flux measurement system based on eddy covariance method according to claim 6, characterized in that: The large flow drainage module also includes: a flow limiting orifice and a second one-way valve; the flow limiting orifice is installed on the shunt pipeline before the vacuum pump; the second one-way valve is installed on the shunt pipeline between the vacuum pump and the flow limiting orifice.

9. The urban area multi-component flux measurement system based on eddy covariance method according to claim 1, characterized in that: The ground multi-component concentration measurement module includes: component concentration measurement module, low-pressure auxiliary drainage sampling module and variable pressure calibration module; The component concentration measurement module includes: a component concentration high-frequency measuring instrument and a workstation; the component concentration high-frequency measuring instrument is used to measure the concentration of the component to be measured in the air at a preset frequency during an observation period; the workstation is connected to the component concentration high-frequency measuring instrument for communication, and the workstation is used to add time information to the concentration, and store the concentration with time information to obtain the concentration time series corresponding to the component to be measured; The low-pressure auxiliary drainage sampling module includes: a low-pressure auxiliary drainage pump; the low-pressure auxiliary drainage pump is installed at the sampling outlet of the component concentration high-frequency measuring instrument, and is used to provide additional sampling flow to assist the sampling process of the component concentration high-frequency measuring instrument; The voltage transformer calibration module is used to perform voltage transformer calibration on the component concentration high frequency measuring instrument; The variable pressure calibration module includes: a calibration pipeline, a pipeline pressure control unit and a standard gas dilution unit, the air inlet end of the calibration pipeline is connected to the standard gas dilution unit, the first air outlet end of the calibration pipeline is connected to the pipeline pressure control unit, and the second air outlet end of the calibration pipeline is connected to the sampling air inlet end of the component concentration high-frequency measuring instrument; the pipeline pressure control unit is used to control the pressure in the calibration pipeline; the standard gas dilution unit is used to provide preset diluted standard gases of different concentrations.

10. A method for measuring multi-component flux in urban areas based on eddy covariance method, applied to the multi-component flux measurement system in urban areas based on eddy covariance method according to any one of claims 1 to 9, characterized in that: The method for measuring multi-component flux in urban areas based on the eddy covariance method comprises: Obtain the vertical wind speed time series and the concentration time series corresponding to each component to be measured during the observation period; For each of the components to be tested, perform the following steps: Dividing the observation period into a plurality of unit times; For each unit time, determine the vertical wind speed sub-time series and the concentration sub-time series corresponding to the component to be measured within the unit time; calculate the covariance sequence corresponding to the unit time based on the vertical wind speed sub-time series and the concentration sub-time series; the covariance sequence includes covariances corresponding to different time lags; Adding the covariance sequences corresponding to all the unit times to obtain a summed covariance sequence, and selecting the time lag corresponding to the maximum value of the summed covariance sequence as the time lag corresponding to the component to be measured; Based on the vertical wind speed time series, the concentration time series corresponding to the component to be measured and the time lag corresponding to the component to be measured, the flux corresponding to the component to be measured is calculated.

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